Sliding banjo cam lock for lathe

ABSTRACT

A mechanism for clamping a banjo (10) toolrest or toolrest bracket to a lathe bed (51) which makes use of a sliding cam (40) which is actuated by a drive shaft (18). The cam is supported independently of the drive shaft by a support block (12) resting on a ledge (14) wich is formed in the base of the banjo. The cam is slidable with respect to the drive shaft along the length of this ledge on the banjo. This structure allows for sturdy clamping with minimal deflection at a predicable catching position along the length of the banjo rest. An eye bolt (20) is used to connect the cam to a clamping plate (22) which is positioned below two, spaced-apart rails (50) extending along the top of the lathe bed. The banjo rest has a generally open bottom (94) through which the shank of the eye bolt extends. Opposite ends of the drive shaft are rotatably supported by end walls (74, 76) of the banjo rest.

FIELD OF THE INVENTION

This invention relates to slide rests suitable for lathes.

BACKGROUND OF THE INVENTION

Lathes are mechanical devices used in the art of carving wood pieces,generally into bowls and other shapes. Lathes are also used for someapplications for the moulding of metals. The lathes operate by spinningwood pieces at high velocity while the operator carves the piece using asharp instrument. The usual lathe has a flat horizontal bed with flathorizontal support rails mounted upon the lathe bed. Vertical supportmembers cam connect the support rails to the lathe bed. A motorized unitfor rotating the wood piece normally extends vertically above the lathebed.

When carving a wood piece it is necessary for the lathe operator to makeuse of a fixed and stable support bar on which the carving instrument issupported while carving the wood piece. Without this support bar itwould be impossible for the operator to have control over the carvinginstrument while working on the object of manufacture.

The support bar is the top member of a toolrest bracket referred to inthe art as a banjo. A banjo consists of a horizontal support which issecured onto the support rails of a lathe bed by way of a clampingmechanism. A vertical portion of the banjo extends upwardly at one end.A top horizontal support bar which is rotatably disposed on the verticalportion of the banjo constitutes the actual toolrest.

Current mechanisms for clamping a banjo to support rails provide forpoor or difficult clamping. These mechanisms typically consist of a boltwhich extends through a slot where the bolt and the slot are bothmovable by the action of a handle which is attached to the bolt and isused to rotate the bolt. Two longitudinal clamps which are closed by theturning of the bolt are used to clamp the banjo to the support rails. Ahandle may be attached to the bolt either above or below the supportrails. In either case, the positioning is awkward for the carpenter andthe clamping effectiveness is often unsatisfactory.

Another design which is currently in use makes use of a cam in order toeffect the clamping action necessary to clamp the banjo to the supportrails. This design makes use of an elongate drive shaft which issupported in the banjo. The shaft has cams and support bearings at eachend of the shaft. A lever is attached to the shaft to rotate the camsfrom an unclamped to a clamped position. In this case the rotation ofthe cams transfer upward movement to the shaft which is in turntransferred to an eye bolt which is moved vertically to pull up on aclamp plate which clamps to the support rails.

This design is problematic in that the drive shaft is subject to adownward pull during the clamping attempt due to the fact that the camsare located on the ends of the drive shaft. As such, when the clampingis to be effected towards the centre of the drive shaft, the drive shaftis prone to bend or deflect. As the drive shaft length is increased thedegree of bending increases proportionally and leads to greaterdeflection.

SUMMARY OF THE INVENTION

The present invention solves these problems by removing the cams fromthe ends of the shaft and providing a cam which is supportedindependently of the drive shaft and which is mounted on the drive shaftsuch that the cam can slide on and with respect to the drive shaft. Thedrive shaft serves to rotate the cam between a clamping and anon-clamping position. An eye bolt is used as a cam receiver and therotation of the cam causes an up or down motion of the eye bolt whichpulls up and releases downwardly the clamp plate, thereby alternatingthe clamp plate between a clamped and an unclamped position. Thisassembly virtually nullifies deflection of the drive shaft at anyclamping position. It is now possible to make larger banjos with longerdrive shafts while preserving effective clamping. In addition, thismechanism allows the cam lever to stop at a consistent and predictableclamp position. This was generally not possible with the prior art.Finally, a much shorter cam throw is possible through zero deflection ofthe cam shaft.

According to one aspect of the invention, a tool supporting apparatusfor use on a lathe comprises a tool supporting device including anelongate bracket having a bottom, said bottom having an elongate,longitudinally extending opening formed therein; an elongate drive shaftrotatably mounted in said bracket and extending longitudinally thereinalong said opening; a clamping mechanism slidably mounted in saidbracket for clamping said tool supporting device rigidly to a bed ofsaid lathe, said clamping mechanism including a rotatable cam memberthrough which said drive shaft extends, a cam supporting membersupported by said bracket, a clamping member, and a connector forconnecting said clamping member to said cam member, said connectorextending through said opening in the bracket, said cam member beingrotatable with respect to said connector, whereby rotation of said cammember by said drive shaft causes said clamping member to move between aclamping position where said bracket is rigidly secured to said bed andan unclamped position, wherein said supporting member acts to supportsaid cam member and thereby prevents movement of said drive shafttowards the bed of the lathe when the clamping member is brought to saidclamping position.

According to a further aspect of the invention, a lathe apparatuscomprises a lathe with a rigid lathe bed having an elongate openingformed therein; a tool supporting device including an elongate brackethaving a bottom surface resting on said lathe bed and an elongate bottomopening extending longitudinally of said bracket; an elongate driveshaft rotatably mounted in said bracket and extending along and abovesaid opening; and a clamping mechanism slidably mounted in or to saidbracket for clamping said tool supporting device rigidly to said lathebed, said clamping mechanism including a cam member slidably mounted onsaid drive shaft and rotatable thereby, a cam supporting membersupported by said bracket, a clamping member disposed in or below saidelongate opening in the lathe bed, and a connector for connecting saidclamping member to said cam member, whereby rotation of said cam memberto a clamping position by said drive shaft causes a portion of saidlathe bed to be clamped between said clamping member and said camsupporting member, said cam member also being rotatable to anon-clamping position which permits the position of said tool supportingdevice to be changed relative to the lathe bed.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings,

FIG. 1 is a cross-sectional view showing the clamping mechanism mountedin a toolrest bracket or banjo, this view taken along the lines I--I ofFIG. 4;

FIG. 2 is a side view of a cam and support block therefor used in thetoolrest bracket of the invention;

FIG. 3 is a right side view of the cam and support block of FIG. 2; and

FIG. 4 is a cross sectional view taken along line IV--IV of FIG. 1.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT

FIGS. 1 to 4 show a clamping mechanism for locking a banjo 10 to thesupport rail or rails of a lathe bed. The banjo 10 is a tool supportingapparatus or tool supporting device. It is an elongate bracket made of ametal such as steel or iron and should be as rigid as possible.

A cylindrical cam 13 is attached to and supported by two bearingportions or members 15. The cam 13 and the coaxial bearing portions ormembers 15 form a continuous hollow cam shaft 40 having a passageway 16of uniform transverse dimensions. These dimensions are those of a squarein the preferred embodiment illustrated. The center axis of the cam 13is offset from and parallel to the axis of the bearing portions. Asupport block 12 has two semi-cylindrical concave support surfaces 17which support the bearing portions 15 of the cam shaft 40. The bearingmembers can easily rotate on the surfaces 17. The support surfaces 17are formed in the top of two cam supporting end sections 96 and 97 ofthe support block 12.

An eye bolt has a head portion 21 connected to a threaded shank portion20. The head portion 21 seats around the cam 13 while the shank portionof the eye bolt extends through a vertically extending opening or hole26 which is situated in the center of the support member 12 between thetwo support surfaces 17. The shank portion extends through an elongate,longitudinally extending opening or slot, located at 94, formed in thebottom of the banjo. The shank portion 20 of the eye bolt is connectedto a clamping member or plate 22 and extends through a bore 25 in theclamping plate 22. The shank portion 20 is threaded into a suitableclamp nut 70 which holds the plate 22 from below.

The eye bolt constitutes a connector for connecting the cam 13 to theclamping plate 22. The camming mechanism includes the cam shaftcomprised of the bearing members 15 and cam 13, support block 12 and theeye bolt. The cam 13 is eccentric with respect to its integral bearingmembers 15 and has a larger diameter than the bearing members. As aresult, when the cam shaft is rotated the cam moves up and down inrelation to the bearing members and in relation to the support block.The up and down movement of the center of the cam is transferred to theeye bolt, causing a generally linear motion in the eye bolt. This motionof the eye bolt causes a corresponding motion of the clamping plate 22.When the cam is rotated away from its bottom dead center position, theclamping plate will move to the clamped position where it is clamped toa bottom of the support rail or rails 50. When the cam is at its bottomdead center position, the clamping plate will be in an unclampedposition with respect to the lathe bed and the banjo will be free tomove longitudinally along an elongate opening 72 formed between therails 50.

FIG. 3 clearly shows the passageway 16 in the interior of the cam shafthaving the cam portion 13 at its center. It can be seen that thepassageway 16 is square shaped in the illustrated embodiment. Thispassageway can have different non-circular shapes provided that thedrive shaft is complementary in shape. The support member 12 has a flatsupport surface 30 formed along each side of the base of the supportmember. The two support surfaces 30 allow the support member to rest ontwo elongate support ledges 14 formed on the base of the banjo.

As shown in FIGS. 1 and 4, drive shaft 18 fits through the passageway 16formed in the interior of the cam shaft 40. When the elongate driveshaft 18 is rotated by pulling manually on a lever or handle 41, whichis attached to a projecting end portion 98 of the drive shaft 18, therotation of the drive shaft rotates cam shaft 40 and therefore cam 13.The resultant rotation of cam 13 actuates the linear motion of the eyebolt causing the clamping plate 22 to move either up or down asdescribed above. The body of the banjo 42 rotatably supports the driveshaft 18 in circular holes formed at opposite ends of the banjo.

It will be understood the square shaft 18 has a round bushing mounted ateach end, these bushings being indicated at 74 and 76. The shaft extendsalong and above the opening 94 in the bottom of the banjo. It will beunderstood that a drive shaft with a circular cross-section can also beused. In this case the drive shaft can be splined in the region of camshaft travel over the length of the drive shaft to prevent the cam shaftfrom rotating relative to the drive shaft.

The banjo has a base 35 with a bottom or bottom surface at 80. Eachledge 14 is machined onto or otherwise formed on each side of the base35 so that the support block 12 is supported by the base. It isimportant to note that the block 12 is supported not by the drive shaft18 but by the ledges 14 located on the base 35. The cam shaft 40 ismounted such that it may slide on the drive shaft 18 while the supportblock 12 is free to slide with the cam shaft along the ledges 14. Assuch the entire clamping mechanism is free to slide in the banjo. Thepreferred banjo is hollow and forms a longitudinally extendingpassageway 82 in which the clamping mechanism can slide.

FIG. 4 illustrates the support block 12 resting on ledges 14 formed onthe base of 35 of the banjo. The banjo 10 is shown resting on supportrails 50 of lathe bed 51, only part of which is shown. It will beunderstood that the lathe itself, apart from the banjo 10, and the lathebed can be of standard design and construction. Because the elongatesupport rails 50 are located at a position between the base of the banjo35 and the clamping plate 22, when the clamping plate is at its upmostposition the banjo 10 is effectively clamped to the support rails 50.When in the clamped position, the banjo 10 is secured tightly to thesupport rails 50 such that one can apply pressure to a tool bar ortoolrest 92 attached to the vertical portion 90 of the banjo without thebanjo slipping. Also because the support block 12 acts to support thecam shaft 40, it thereby prevents any significant movement or deflectionof the drive shaft towards the bed of the lathe when the clamping plateis brought to the clamping position.

As will be apparent to those skilled in the art in the light of theforegoing disclosure, alterations and modifications are possible in thepractice of this invention without departing from the spirit or scopethereof. Accordingly, the scope of the invention is to be construed inaccordance with the substance defined by the following claims.

I claim:
 1. A tool supporting apparatus for use on a lathe, saidapparatus comprising:a tool supporting device including an elongatebracket having a bottom, said bottom having an elongate, longitudinallyextending opening formed therein; an elongate drive shaft rotatablymounted in said bracket and extending longitudinally therein along saidopening; and a clamping mechanism slidably mounted in said bracket forclamping said tool supporting device rigidly to a bed of said lathe,said clamping mechanism including a rotatable cam member through whichsaid drive shaft extends, a cam supporting member supported by saidbracket, a clamping member, and a connector for connecting said clampingmember to said cam member, said connector extending through said openingin the bracket, said cam member being rotatable with respect to saidconnector, whereby rotation of said cam member by said drive shaftcauses said clamping member to move between a clamping position wheresaid bracket is rigidly secured to said bed and an unclamped position,wherein said supporting member acts to support said cam member andthereby helps to prevent movement of said drive shaft towards the bed ofthe lathe when the clamping member is brought to said clamping position.2. A tool supporting apparatus according to claim 1 wherein said camsupporting member is a support block having two flat support surfacesformed on opposite sides thereof and said bracket is formed with twoelongate support ledges located on opposite sides of the elongateopening in said bracket, said ledges engaging said support surfaces andacting to support said support block.
 3. A tool supporting apparatusaccording to claim 1 wherein said elongate bracket has two oppositeends, said drive shaft is rotatably mounted in holes formed in saidopposite ends, and an elongate passageway extends between said oppositeends, said clamping mechanism being slidable along said passageway.
 4. Atool supporting apparatus according to claim 1 wherein said connectorcomprises an eye bolt having a threaded shaft portion and a threaded nutmember attached to said shaft portion and holding said clamping member,said shaft portion extending through a hole in said clamping member. 5.A tool supporting apparatus according to claim 1 wherein said driveshaft has an end portion projecting from one end of said bracket and alever is attached to said end portion to provide manual means forrotating said drive shaft.
 6. A tool supporting apparatus according toclaim 1 wherein said cam member includes a cylindrical, central camportion and two cylindrical coaxial bearing portions located on oppositesides of said cam portion, a center axis of said cam portion beingoffset from and parallel to the axis of said bearing portions, whereinsaid bearing portions engage two concave support surfaces formed on saidcam supporting member.
 7. A tool supporting apparatus according to claim2 wherein said support block has a vertically extending central holeformed therein and two cam supporting end sections located on oppositesides of said central hole and wherein said connector comprises an eyebolt with a threaded shaft that extends through said central hole,through said opening in the bracket, and through a hole in said clampingmember.
 8. A tool supporting apparatus according to claim 7 wherein saidcam member comprises a cylindrical, central cam portion and twocylindrical coaxial bearing portions located on opposite sides of saidcam portion, a center axis of said cam portion being offset from andparallel to the axis of said bearing portions, and wherein said bearingportions engage curved support surfaces formed on said cam supportingend sections and the cam member is supported thereby when said clampingmember is moved to the clamping position.
 9. A tool supporting apparatusaccording to claim 1 wherein said drive shaft has a non-circular,uniform cross-section along a substantial portion of its length and saidcam member has a shaft-receiving passageway formed therein, thispassageway having a matching, non-circular cross-section, and whereinsaid clamping mechanism is slidable along said substantial portion ofthe shaft.
 10. A tool supporting apparatus according to claim 1 whereinsaid clamping member is a flat metal plate having a hole therein andsaid connector includes an eye bolt with a threaded shaft portion thatextends through said hole in the metal plate.
 11. A lathe apparatuscomprising:a lathe with a rigid lathe bed having an elongate openingformed therein; a tool supporting device including an elongate brackethaving a bottom surface resting on said lathe bed and an elongate bottomopening extending longitudinally of said bracket; an elongate driveshaft rotatably mounted in said bracket and extending along and abovesaid bottom opening; and a clamping mechanism slidably mounted in or tosaid bracket for clamping said tool supporting device rigidly to saidlathe bed, said clamping mechanism including a cam member slidablymounted on said drive shaft and rotatable thereby, a cam supportingmember supported by said bracket, a clamping member disposed in or belowsaid elongate opening in the lathe bed, and a connector for connectingsaid clamping member to said cam member, whereby rotation of said cammember to a clamping position by said drive shaft causes a portion ofsaid lathe bed to be clamped between said clamping member and said camsupporting member, said cam member also being rotatable to anon-clamping position which permits the position of said tool supportingdevice to be changed relative to the lathe bed.
 12. A lathe apparatusaccording to claim 11 wherein said connector comprises an eye bolthaving a threaded shaft portion and a threaded nut member attached tosaid shaft portion and holding said clamping member, said shaft portionextending through a hole in said clamping member.
 13. A lathe apparatusaccording to claim 11 wherein said lathe bed includes two flat topped,spaced apart support rails with said elongate opening in the bed beingformed between said rails and wherein, in said clamping position, saidclamping member presses against bottom surfaces of said support rails.14. A lathe apparatus according to claim 11 wherein said cam supportingmember is a support block having two flat support surfaces formed onopposite sides thereof and said bracket is formed with two elongatesupport ledges located on opposite sides of the elongate bottom openingin said bracket, said ledges engaging said support surfaces and actingto support said support block.
 15. A lathe apparatus according to claim11 wherein said elongate bracket has two opposite ends, said drive shaftis rotatably mounted in holes formed in said opposite ends, and anelongate passageway extends between said opposite ends, said clampingmechanism being slidable along said passageway.
 16. A tool supportingapparatus for use on a lathe having a lathe bed, comprising:a roundedcam shaft having a passageway formed therein of uniform dimension, saidpassageway extending through the entire length of said cam shaft, saidcam shaft having two rounded end pieces forming bearing members at eachend thereof, said shaft also having a cam located between the bearingmembers eccentric to the bearing members; a support block having two endsections, each end section forming a concave support surface whichsupports one of said bearing members of said cam shaft, said supportblock having a central opening between said end sections; an eye boltmember having a generally circular head and a threaded shank, whereinthe head extends around said cam and wherein said shank extends throughsaid opening of the support block; a drive shaft extending through saidpassageway in said cam shaft, said cam shaft being slidably disposed onsaid drive shaft; an elongate support bracket having two opposite endsrotatably supporting said drive shaft, said bracket having at least oneledge formed thereon which supports said support block, said supportblock being slidably disposed on said at least one ledge; and a clampingplate which is connected to said shank of said eye bolt member whereinduring use of said apparatus, said clamping plate can be pulled by therotation of the cam to a clamping position where the clamping plate isin clamping contact with said lathe bed.
 17. A tool supporting apparatusaccording to claim 16 wherein the support bracket is slidable withrespect to the lathe bed when said clamping plate is in an unclampedposition and said support bracket has a toolrest mounted thereon.
 18. Atool supporting apparatus according to claim 16 wherein a handle isattached to one end of said drive shaft for imparting a rotationalmotion to the drive shaft.
 19. A tool supporting apparatus according toclaim 16 wherein said support bracket has a bottom with an elongateopening formed therein and two ledges are formed along opposite sides ofsaid elongate opening, each ledge supporting one side of said supportblock.
 20. A tool supporting apparatus according to claim 16 whereinsaid support bracket is hollow and forms an elongate, open-bottompassageway extending between said opposite ends, and said cam shaft,support block, and eye bolt member are slidable along said passageway.